I dont know why it don't work, when I try the following it work!
<menuitem id="dietfacts_menu" action="product.product_template_actions_dietfacts" name="Diet Items" parent="base.menu_custom"/>
But, when I change the parent attribute to base.menu_sales It don't work!!
<menuitem id="dietfacts_menu" action="product.product_template_actions_dietfacts" name="Diet Items" parent="base.menu_sales"/>
on Odoo 9, the both codes work very well, but on odoo 10, only the first!!
please help!!
The problem lies in the XML ID you are providing to the parent.
To get the correct XML id of the menu item go Settings -> Dashboard -> Activate Developers Console
Navigate to Technical -> User Interface -> Menu Items.
Locate the parent menu by searching for it. Open it up. Click on the debugger menu present above and click over the View Metadata option.
This will show you the correct XML ID of the menu, which you can write in the parent option of the menuitem.
Hope it helps. Thanks